(a) Field of the Invention
The present invention relates to a cleaning/drying station and a semiconductor device production line having the cleaning/drying station. More particularly, the present invention relates to a cleaning/drying system in a semiconductor device production line in which two different cleaning treatments (i.e., performances of cleaning) and two different drying treatments (i.e., performances of drying) can be selected with a high degree of flexibility, as well as to a production line for semiconductor devices having such a cleaning/drying system in which the layout or arrangement of cleaning devices and drying devices is optimized.
(a) Description of the Related Art
During fabrication of semiconductor devices, a cleaning treatment for wet-cleaning a wafer and a drying treatment for drying the wafer subsequent to the cleaning treatment are conducted before and after each of various processing treatments performed on the wafer.
For example, when a wafer is dry-etched, a cleaning treatment is first performed in order to remove contaminants from a dry-etched wafer surface, and a drying treatment is performed in order to dry the cleaned wafer. Such a cleaning treatment is almost inevitably performed before and after each processing treatment; e.g., before formation of a silicon oxide film on a wafer, after ion implantation, and before epitaxal growth. That is, in many cases, a cleaning treatment is performed between two successive processing treatments. Further, a drying treatment is generally performed after the cleaning treatment. In general, the cleaning treatment includes a chemical cleaning step for cleaning a wafer by use of chemical solution, and a rinse cleaning step for removing, by use of a rinsing liquid, the chemical solution remaking on the wafer.
A typical example of combined of a chemical cleaning step and a rinse cleaning step is an RCA cleaning process. The RCA process includes: a first step in which a wafer is cleaned by use of a mixed cleaning solution containing ammonium, hydrogen peroxide and water in predetermined ratios, followed by rinsing by use of purified water; a second step in which the wafer is immersed into a diluted-HF solution, followed by rinsing by use of purified water; and a third step in which a wafer is cleaned by use of a mixed solution containing hydrochloric acid, hydrogen peroxide and water in predetermined ratios, followed by rinsing by use of purified water.
Also, there is known a specific cleaning method in which both a native oxide film and metal contaminants are removed from a wafer through use of aqueous solution of hydrofluoric acid or hydrofluoric acid-hydrogen peroxide cleaning solution containing 0.5% hydrofluoric acid and 1-10% hydrogen peroxide, followed by rinsing the wafer by use of pure water.
In this text, processing by use of such a hydrofluoric acid based chemical solution will be referred to as xe2x80x9ccleaning by use of an HF (cleaning) solution,xe2x80x9d and processing by use of non-hydrofluoric acid based chemical solution such as alkaline cleaning, acid cleaning, or RCA cleaning will be referred to as xe2x80x9ccleaning by use of a non-HF (cleaning) solution.xe2x80x9d
Conventionally, a drying treatment after cleaning has been performed by use of a spin drying device. In the spin drying device, a cleaned wafer is rotated at a high speed in order to remove water remaining on the wafer after a rinsing step, by the effect of centrifugal force and air flow. The spin drying device can dry wafers at a high throughput, but cannot remove water completely, resulting in formation of water marks and the like on a wafer. The spin drying device is a typical example of a high throughput/low performance drying device and is mainly used in a drying treatment after a cleaning treatment performed by use of a non-HF cleaning solution, wherein a high drying performance is not generally required.
Conventional spin drying devices are classified into three types; i.e., a multi-cassette dryer, a single-cassette dryer, and a single-wafer dryer. An example of the single-cassette spin dryer is of a rotation-type in which, as shown in FIG. 1, a single cassette xe2x80x9cCxe2x80x9d carrying wafers xe2x80x9cWxe2x80x9d is received in a drum xe2x80x9cDxe2x80x9d, which is rotated about an eccentric axis xe2x80x9cExe2x80x9d An example of the multi-cassette spin dryer is of a revolution-type in which, as shown in FIG. 2, two cassettes xe2x80x9cKxe2x80x9d each carrying wafers xe2x80x9cWxe2x80x9d are received in a drum xe2x80x9cDxe2x80x9d to be located at diametrically opposite positions, and the drum xe2x80x9cDxe2x80x9d is rotated about a vertical rotational axis xe2x80x9cF.xe2x80x9d
With an increase in the wafer deter for the semiconductor devices, a decrease in element dimensions and employment of multi-level wiring, the surface profile of the wafer including projections and depressions on the wafer surface has become finer and the level difference in the profile has increased. Thus, the aspect ratio of via holes has increased. Therefore, it has become difficult to dry wafers to a desired drying level by a spin drying method, resulting in occurrence of problems such as generation of water marks on the wafer surface, and an increased contact resistance of a via hole stemming from incomplete drying of the bottom portion of the via hole.
In order to solve the above-described problems, an IPA vapor drying technique making use of IPA (isopropyl alcohol) has recently come into practical use. As shown in FIG. 3, in an IPA vapor drying device using the IPA vapor drying technique, water droplets or a water film remaining on a wafer is replaced with condensed IPA, which is then allowed to drop and evaporate eventually. Thus, the wafer is dried.
Since the IPA vapor drying device (hereinafter simply referred to as an xe2x80x9cIPA drying devicexe2x80x9d) can almost completely replace water on a wafer with IPA and the IPA can evaporate after replacement, water marks are less likely to be generated. The IPA drying device is a typical example of a high performance/low throughput dryer and is used mainly in a drying treatment after a cleaning treatment making use of an HF cleaning solution, wherein a high drying performance is generally required Further, there has been developed a direct IPA drying method utilizing an integrated apparatus including a cleaning device and a drying device. In this method, cleaning, rinsing, and drying are performed within a closed space in order to minimize exposure of a wafer to an oxidizing atmosphere, which exposure would otherwise occur when the wafer is transported from a rinsing stage to a drying stage.
In a conventional production line for semiconductor devices, in order to secure a high throughput of a drying treatment, a high throughput/low performance drying device is provided after a cleaning treatment by use of non-HF cleaning solution, such as alkali cleaning, acid cleaning or RCA cleaning, which does not require a wafer to be dried to a high degree. On the other had, in order to secure a high quality of the drying treatment, a low throughput/high performance drying device is provided after a cleaning treatment, such as a chemical cleaning treatment making use of an HF cleaning solution.
With reference to FIG. 4, a conventional production line for semiconductor devices will be described. The conventional production line 90 includes a series of processing stations 92A-92E each performing a predetermined processing treatment on a wafer. A wafer is transported to the processing stations 92A-92E and is successively subjected to the respective processing treatments in the processing stations 92A-92E. In the production line 90, a cleaning/drying treatment must be performed for a wafer before and/or after the processing treatment at each processing station 92.
For example, in a step for forming a gate oxide film, an oxide film is wet-etched, and then a nitride film is wet-etched. During the wet etching of the oxide film, contaminants are dissolved into rinse droplets, resulting in contamination of a wafer surface. In order to suppress such contamination, a wafer is generally cleaned by use of an HF cleaning solution, and is subjected to IPA drying. Further, when plugs are formed in an inter-layer dielectric film on a wafer such that the plugs penetrate the dielectric film, the dielectric film is etched to form contact holes, which are then cleaned by use of a non-HF cleaning solution, and the wafer is subjected to spin drying. In such a process, in order to suppress generation of water marks, the wafer is cleaned by use of an HF cleaning solution and is then subjected to IPA dryimg.
In the production line 90, a cleaning treatment making use of an HF cleaning solution and a high performance drying treatment are conducted after the processing treatments performed at the processing stations 92A and 92D. Further, a cleaning treatment making use of a non-HF cleaning solution and a low performance drying treatment are conducted after the processing treatments performed at the processing stations 92B and 92C.
Therefore, in the conventional production line 90, a cleaning device 94 using an HF cleaning solution and an IPA drying device 96 are provided after each of the processing stations 92A and 92D, and a cleaning device 98 using a non-HF cleaning solution and a spin drying device 100 are provided after each of the processing stations 92B and 92C.
The conventional production line for semiconductor devices as described above involves the following problems.
First, each processing station is equipped with a combination of an HF cleaning device and a high performance drying device or a combination of a non-HF cleaning device and a low performance drying device. Therefore, flexibility in selection of cleaning treatments and drying treatments is low. For example, in order to cope with an increase in wafer diameter, a decrease in element dimensions and employment of multi-level wiring, the conventional cleaning condition which does not require HP cleaning solution is changed to the cleaning condition which requires HF cleaning solution. However, since only a combination of a non-HF cleaning device and a spin drying device is provided downstream of the relevant processing station in the conventional production line for semiconductor devices, the cleaning conditions are extremely difficult to change.
Further, when a low performance drying device is provided, drying cannot be performed to a sufficient degree after an HF processing treatment or the like which requires a high degree of drying, resulting in a problem occurring in subsequent steps. On the contrary, when a high performance drying device is provided despite only a low degree of drying being required, the throughput of the entire production line for semiconductor devices decreases, resulting in an increased production cost. If two kinds of drying devices; i.e., a high performance drying device and a low performance drying device, are employed in order to solve the problems described above, facility costs increase
Second, there is a problem in that the throughput of the production line for semiconductor devices depends on the throughput of a drying device. For example, when a high performance drying device is provided, the throughput of the high performance drying device substantially determines the throughput of the entire production line for semiconductor devices.
Third, when a cleaning device and a drying device are provided before or after each processing station, a huge number of cleaning devices and drying devices are needed. Therefore, the facility costs of the cleaning and drying devices have been high, and costs involved in cleaning and drying wafers have been high. In addition, since only in rare cases do all the cleaning and drying devices operate at all times, the idle times of the cleaning and drying devices have been long.
In view of the problems involved in the conventional production line for semiconductor devices and in consideration of requirements for producing next generation wafers of 300 mm diameter, a cleaning device and a drying device must be provided in a production line in such a way as to improve the quality of cleaning and drying treatments for wafers, to decrease cleaning/drying cost, and to improve the flexibility of the treatments.
In view, of the foregoing, an object of the present invention is to provide a cleaning/drying system that provides cleaning and drying treatments in a highly flexible manner.
Another object of the present invention is to provide a production line for semiconductor devices that is optimized to increase the flexibility of cleaning and drying treatments.
The present invention provides a cleaning/drying system comprising a first cleaning device for cleaning a wafer by using an HF cleaning solution, a second cleaning device for cleaning a wafer by using a non-HF cleaning solution, a high-performance drying device for drying a wafer, and a high-speed drying device for drying a wafer at a higher speed and with a lower degree of drying than the high-performance drying device, wherein the first cleaning device and the second cleaning device is selected based on desired conditions for cleaning, and the high-performance drying device and the high-speed drying device is selected based on desired conditions for drying.
The present invention also provides a production line comprising: a series of processing stations each for processing a wafer in the production line based on a desired treatment; a cleaning/drying station including a first cleaning device for cleaning a wafer by using an HF cleaning solution, a second cleaning device for cleaning a wafer by using a non-HF cleaning solution, a high-performance drying device for drying a wafer, a high-speed drying device for drying a wafer at a higher speed and with a lower degree of drying than the high-performance drying device, wherein the first cleaning device or the second cleaning device is selected based on desired conditions for cleaning, and the high-performance drying device or the high-speed drying device is selected based on desired conditions for drying; a wafer transport system for transporting a wafer between each of the processing stations and the cleaning/drying station.
In accordance with the cleaning/drying system and the production line of the present invention, flexibility of selection of the cleaning device and the drying device can be improved substantially without increasing costs or space for the production line.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.